There is a need in the technical field of transporting powder and/or granular material to provide a powder isolating valve to cut off and seal powder and/or granular material flow from storage hoppers and bins.
This is traditionally done with commonly known slide valves. There are various styles and configurations of slide valves but they all suffer from either leakage, jamming or a combination of both of these problems. This is a well know problem for the powder handling industry and at the present time there is no satisfactory solution. In addition, jamming with powder is a particular problem with larger valves above 300 mm diameter where large actuators are required to overcome the friction in slide valves.
Other types of valve are used such as butterfly valves but they can be difficult to turn in a packed head of material and the blade is an obstruction to flow. Inflatable seal valves with a spherical closure member are an alternative but are expensive, heavy and the valve sealing systems are expensive to produce with larger sizes requiring special moulds for rubber seals. The machined parts surrounding moulded inflatable valve seals are close tolerance intricate shapes and are therefore expensive to produce.
For powder isolation it is not necessary to provide a gas tight seal through the valve but powder should not be able to pass through the valve. It is however necessary to provide a good seal for gas and powder to the outside of the valve. One of the big disadvantages of slide valves is that it is difficult to stop the blade from dragging material out as the valve opens. The blade can also lead to leakage of powder. Another difficulty with large size slide valves with flat blades is making the valves strong enough to resist failure in the event of an internal dust explosion. It is a requirement to have a containment design which is capable of dealing with an internal explosion due to the explosion risk of combustible material being transported such as coal dust. This is relatively easy to achieve with a spherical closure member.
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide a powder isolating valve which is capable of sealing valves from powder leakage during the transport of powder and/or granular material.